Lowering LVC on YK33F 48V controller

[TMaster]

Hello, I'm adding some more series cells to my setup, but the 48V controller I have the LVC is too high for my pack, and will shut down at about 3.23V per cell. Under 40 amps of load throttling I calculated with voltage sag will only get me 60% of the pack useage. (42V LVC) (13S lithium pack) I have the exact same controller thats a 36V version that shuts down at 31.5V. It seems there is only 5 resistors that are different on the entire board between the two. I'm assuming I can pull the 36V resistors in those area's and put them on the 48V board, I know a better solution would be to figure it out and put in resistors to make the LVC cut out at 3.0V with that pack, and not 2.41V where it will be if I just swap. But I am ok with the LVC being to low, I can manage it manual watching the capacity and voltage on the Display I have. Should I just swap them all or do you guys know which ones exactly to do? Or if you know how I can change them out so its close to 3.0V per cell? Thanks

YK33F controller board... Check out the big R002 resistor as a Shunt.

 

[TMaster]

Ok I traced the board, and the two little 155ohm resistors go to the sport mode switch so those have nothing to do with the LVC. So the only thing left are the two through hole resistors and the little SMD under on the 36V version. Turns out those resistors are in parallel. There is a trace under the board connecting them along with other two ends connecting them on the top of the board. The 36V controller is making 36.5k (39k & 1M & 2M) total resistance there, and the 48V controller is making 49.1k (50k & 3M resistor)

After doing some calculating, I came up with about a 1.16 as a divider ratio to figure out the resistance need with the LVC voltage value. I think!

36.5k / 1.16 = 31.5V LVC
49.1k / 1.16 = 42V LVC

So to get that 39V LVC, I need 46k ohms. That would put it at 3.05V per cell.

Let me know if that looks right to you guys, The resistances may be off a few %. Now I just have to go find a resistor combination or put in a single 46k resistor.

 

[Ian444]

On the 48V controller, you could simply replace the 3M resistor with a 750k resistor to get 46.1k total. I used this online calc https://www.electronics2000.co.uk/calc/series-parallel-resistor-calculator.php

 

[TMaster]

Thanks, I decided to go with a 49.9k and 560k resistors, that put it at about 45.8k, and 3.03V per cell outcome. The cells I have are LG 18650 MH1's, and the cutoff is 2.5V so it will be fine. I also swapped the big power resistor from a 1.2k ohm to a 1.5k ohm, because the voltage at full charge after that resistor going into the 78L15 SMD regulator was just over 39V (full pack charge 54V). I was hoping to get it down to 35V with that resistor swap, but it only dropped it to 38V .... LOL. When the pack is at (39-40) LVC, it will be about 22V going into the regulator so that is fine. I am sure that little regulator does not use that many milliamps to run.